as I noted above, I had xcas 1.1.4-19 (c) 2000-14
now I've installed 1.2 unstable and with the general equation I get
\[ \frac{\mathrm{c\_1} \sin\left(x\right)-\mathrm{c\_2} \cos\left(x\right)-\mathrm{c\_1}\cdot x \cos\left(x\right)-\mathrm{c\_2}\cdot x \sin\left(x\right)}{\mathrm{c\_1} \cos\left(x\right)+\mathrm{c\_2} \sin\left(x\right)} \]
then, with trigtan() ->